In association with rapid expansion of needs for optical communications, substantial increase in a transfer capacity has been required. So far increase of transfer capacity has been realized with increase in a processing speed according to a synchronous digital hierarchy (SDH), namely with introduction of time division multiplexing (TDM). Today the maximum value in the practical transfer rate is 10 Gbit/s. This is a limit speed processable in an electronic circuit for commercial use, which causes increase in costs for a transfer path terminal device.
On the other hand, in association with progress in the laser diode (LD) manufacturing technology as well as with smoothing of a gain for an erbium dope optical fiber amplifier (EDFA), a wavelength division multiplexing system has been gathering intense attentions from related people. In this system, light signals having different wavelengths are used as carrier waves, a transfer speed for one wave is suppressed at a low level, and existing types of transfer path terminal devices can be used, which makes it possible to suppress costs for the entire system.
Also if each station device is formed with light receiving circuit parts, all station devices are connected with an optically transparent medium not including a process for conversion between electricity and light. Conventionally switching of a transfer path is executed by means of converting light to electricity or converting electricity to light and also by terminating a signal to read path information and electrically switching path connection, but if the WDM technology is used, it is possible to easily switch a transfer path not by means of converting light to electricity, nor by converting electricity to light. This allows simplification of maintenance and administration management of a network.
As a wavelength multiplexed light communication device required in various types of network using the WDM technology, it is possible to enumerate (1) a light branch circuit used in a bus type of network, (2) an add/drop multiplexing circuit used in a ring-type network, and (3) a bidirectional wavelength multiplexing/separating circuit used in a star-type network.
In the submarine cable system, an optical branch circuit for branching an optical cable running in one direction to two branches running in different directions respectively has been required. So far an optical branch circuit having a two-conductor optical cable for each destination has been used, but in this case totally four conductors, two for an up-link channel and remaining two for a down-link channel, have been required, which causes increase in weight of an optical cable as well as in costs thereof. In contrast, by using the WDM technology, a number of required conductors can be reduced to a half, as described in "Optical Submarine Cable Communication" supervised by Noboru Oyama, Moriji Kuwabara, KEC, pp.141-151, 1991.
FIG. 28 shows an example of an optical branch circuit using the WDM technology. In this figure, designated at the reference numeral 300 is an optical branch circuit, at 301a, 301b, and 301c are optical filters each for dividing a wavelength, at 302a, 302b, and 302c are optical filters each for synthesizing a wavelength. For instance, light waves having a wavelength of .lambda.1 and .lambda.2 introduced from the cable A are separated from each other by the optical filter 301a, and the light wave having a wavelength of .lambda.1 goes through the optical filter 302c into the cable C and the light wave having a wavelength of .lambda.2 goes through the optical filter 302b into the cable B. On the other hand, light waves having a wavelength of .lambda.1 and .lambda.2 respectively introduced from the cable B are separated from each other by the optical filter 301b, and the light wave having a wavelength of .lambda.1 goes through the optical filter 302a into the cable A, while the light wave having a wavelength of .lambda.2 goes through the optical filter 302c into the cable C. Thus, by using two different wavelengths, branching of an optical cable to two directions becomes possible.
By the way, in the optical filters 301a, 301b, 301c, 302a, 302b, and 302c each playing an important role in this optical branch circuit, the dielectric multilayered film filter as shown in FIG. 29 has been used in most cases.
Next, a description is made for operations of the dielectric multilayered film filter with reference to FIG. 29. In this figure WDM light coming in from a terminal 290 is collimated by a lens 291a and reaches the dielectric multilayered film 292. This dielectric multilayered film 292 is designed so that it reflects, for instance, a light wave having a wavelength of and passes light waves having other wavelengths. The reflected light wave having a wavelength of .lambda.1 is focused by the lens 291b and sent to a terminal 290b. A light receiver 294 is connected to this point. On the other hand, a light transmitter 293 for a light wave having a wavelength of .lambda.5 is connected to a terminal 290c, the light wave passes through the lens 291c, dielectric multilayered film 292 and is outputted to the terminal 290a.
As a concrete example of the ring type of network, there is, for instance, the add/drop mutiplexer (ADM) network based on the WSM technology described in "M. J.Chawki, V. Tholey, E. Delevaque, S. Boj and E. Gay, `Wavelength reuse scheme in a WDM unidirectional ring network using a proper fiber grating add/drop multiplexer`, Electronics Letters, vol. 31, No.6, pp. 476-477, 1995". The ADM indicates a multiplexer which drops a signal to a station and at the same time add a signal transmitted from the station to other station.
A network connected with a ring type of optical fiber is connected through an optical cross-connect device to other network. For instance, a light wave having a specific wavelength of .lambda.1 is allocated to a station 1. Of the WDM signals arriving in the station 1, only a light wave having a wavelength of .lambda.1 transmitted to the station is branched by an optical filter and is received by a light receiver. On the other hand, a signal transmitted from a light transmitter in the station 1 is added to the optical fiber using a light wave having a wavelength of .lambda.1 as a carrier wave. To which station each light wave has been transmitted can be recognized by checking a wavelength of each light wave. Similarly a light wave having a specific wavelength of .lambda.2 is allocated to a station 2.
FIG. 30 shows an example of a wavelength multiplexed light transfer device according to the conventional technology which has been proposed as an optical filter required for a ring type of network. The basic principle of this type of optical filter was described in "K. 0. Hill, D. C. Johnson, F. Bilodeau, S. Faucher, 1 Narrow-bandwidth optical waveguide transmission filters`, Electronics Letters vol. 23, No.9, pp.465-466, 1987", and then was described more detailedly in "D. C. Johnson, K. O. Hill, F.Bilodeau, S. Faucher, `New design concept for a narrow band wavelength-selective optical tap and combiner` Electronics Letters vol. 23, No.13, pp.668-669, 1987". The same contents is also described in U.S. Pat. No.4,900,119. A similar invention is described in Japanese Patent Laid-Open Publication No. 96605/1989.
In FIG. 30, designated at the reference numerals 310a, 310b is a fiber grating, at 311a and 311b is a 2.times.2 3-dB coupler, at 312 a light transmitter, and at 313 a light receiver. Also designated at the reference numerals 314a, 314b is a refractive index adjusting section, at 315a, 315b a terminal in the front stage of the 3-dB coupler 311a, at 315c, 315d a terminal in the rear stage of the 3-dB coupler 311a, at 316a, 316b a terminal in the front stage of the 3-dB coupler 311b, and at 316c, 316d a terminal in the rear stage of the 3-dB coupler 311b.
The fiber grating was invented by K. O. Hill et al. working in Communication Research Center in Canada, and when an optical fiber is exposed to an ultraviolet ray from outside, a lattice defect is caused and cyclic fluctuation of a refractive index occurs, so that a fiber grating works as a wavelength selective reflector. The fiber grating is characterized in that the wavelength reproducibility is high and the insertion loss is extremely low.
Assuming that a grating pitch of the fiber grating is .LAMBDA., an equivalent refractive index of the fiber is neff, an effective grating length is Leff, and a coupling coefficient is .kappa., a central wavelength .lambda.B of the Bragg's reflection is equal to .LAMBDA./neff (.lambda.B=.LAMBDA./neff), while a reflection coefficient R at a central wavelength of the reflected light is equal to tanh 2 (.kappa.Leff).
For convenience of description, it is assumed herein that a Bragg's wavelength (a wavelength of a reflected light wave) for the fiber gratings 310a, 310b in this example of the conventional technology has been set to .lambda.5. The fiber grating itself works only as a wavelength selective reflector, but when the 3-dB coupler 311a is connected to a front stage thereof, of the WDM light waves coming in from the terminal 315a, only the light wave having a wavelength of .lambda.5 is reflected by the fiber grating, and can be taken out from the terminal 315b of the 3dB coupler.
The light coming in from the terminal 315a is divided to two portions, which are sent to the terminals 315c, 315d respectively. The light waves coming out from the terminals 315c, 315d are reflected by the fiber gratings 310a, 310b respectively and return to the 3-dB coupler 311a again, but when returning from the terminal 315a to the terminal 315a, a light wave flowing through the first route comprising the terminal 315a, terminal 315c, fiber grating 310a (reflection), terminal 315c, and terminal 315a in this order is synthesized with a light wave flowing through a second route comprising the terminal 315a, terminal 315d, fiber grating 310b (reflection), terminal 315d, and terminal 315a in this order, and the synthesized light wave goes out from the terminal 315a, but a phase difference of .pi./2 between a light wave passing through the coupler and the coupled light wave is generated in the 3-dB coupler, so that a phase difference of .pi. is generated between the transmitted light waves passing through the light paths from the terminal 315a to the terminal 315c and from the terminal 315c to the terminal 315a in the first route and between the coupled light waves passing through the light paths from the terminal 315a to the terminal 315d and from the terminal 315d to the terminal 315a in the second route, and a phase of the light in the first route is reverse to that of the light in the second route, so that interference between the light waves is canceled.
When returning from the terminal 315a to the terminal 315b, a light wave flowing through a first route comprising the terminal 315a, terminal 315c, fiber grating 310a (reflection), terminal 315c, and terminal 315b in this order is synthesized with a light wave flowing in a second route comprising the terminal 315a, terminal 315d, fiber grating 310b (reflection) terminal 315d, and terminal 315b, and the synthesized light wave goes out from the terminal 315b, but a light wave running from the terminal 315a to the terminal 315c in the first route is a transmitted light wave and a light wave running from the terminal 315c to the terminal 315b in the first route is a coupled light wave, while in the second route a light wave running from the terminal 315a to the terminal 315d is a coupled light wave and that running from the terminal 315d to the terminal 315b is a transmitted light, and thus a phase delay of .pi./2 is generated in both the light waves running in the first and second routes, meaning that the total phase delay is .pi., and an interference between the light waves is intensified. For this reason, the light wave having a wavelength .lambda.5 from the terminal 315a is sent to the terminal 315b.
Light waves each having a wavelength other than .lambda.5 and not reflected by the fiber grating reach the 3-dB coupler 311b, but when sent from the terminal 315a to the terminal 316c, a light wave running through the first route comprising the terminal 315a, terminal 315c, fiber grating 310a (transmission), terminal 316a and terminal 316c in this order is synthesized with a light wave running through the second route comprising the terminal 315a, terminal 315d, fiber grating 310b (transmission), terminal 316b, and terminal 316c, and the synthesized light wave goes out of the terminal 316c, but a light wave passing through the light paths from the terminal 315a to the terminal 315c and from the terminal 316a to the terminal 316c in the first route is a transmitted light wave, while the light wave passing through the light paths from the terminal 315a to the terminal 315d and from the terminal 316b to the terminal 316c in the second route is a coupled light wave, so that a phase difference of .pi. is generated, and a phase of the light wave running through the first route is reverse to that of the light wave running through the second route, so that interference between the light waves is canceled.
When sent from the terminal 315a to the terminal 316d, a light wave running through a first route comprising the terminal 315a, terminal 315c, fiber grating 310a (transmission), terminal 316a, and terminal 316d is synthesized with a light wave running through a second route comprising the terminal 315a, terminal 315d, fiber grating 310b (transmission), terminal 316b, and terminal 316d, and the synthesized light wave goes out of the terminal 316d, but in the first route a light wave passing through the light path from the terminal 315a to the terminal 315c is a transmitted light wave and a light wave passing through the light path from the terminal 316a to the terminal 316d is a coupled light wave, while in the second route a light wave passing through the light path from the terminal 315a to the terminal 315d is a coupled light wave and that passing through the light path from the terminal 316a to the terminal 316d is a transmitted light wave, so that a common mode by a phase delay of .pi./2 is generated between the light wave running through the first route and that running through the second route, and the light waves is intensified by this interference. For this reason, light waves each coming in from the terminal 315a and having a wavelength other than .pi.5 is sent to the terminal 316d.
On the other hand, a signal having a wavelength of .pi.5 to be inserted is transmitted from the light transmitter 312 connected to the terminal 316c and is set to the terminal 316d. The operations are the same as those in a case when a light wave coming in from the terminal 315a and having a wavelength of .lambda.5 is sent to the terminal 315b. For this reason, a light wave coming in from the terminal 315a and having a wavelength other than .lambda.5 is sent to the terminal 316d.
It should be noted that the refractive index adjusting section 314a adjusts a refractive index so that a length of each light path from the 3-dB coupler 311a to each of the fiber gratings 310a, 310b will be identical. Also the refractive index adjusting section 314b adjusts a refractive index so that a length of each light path from the 3-dB coupler 311b to each of the fiber gratings 310a, 310b will be identical.
The refractive index adjusting sections 314a, 314b can adjust a refractive index by means of exposure to a ultraviolet ray like in the method of manufacturing a fiber grating. This technology is described in Japanese Patent Laid-Open No. 298702/1992.
Concrete examples of the star-shaped network include the LAMBDANET. Detailed description thereof is provided in "M. S. Goodman, H. Kobrinski, M. P. Vecchi, R. M. Bulley, and J. L. Gimlett, IEEE Journal of Selected Areas in Communications, vol. 8, p.995, 1990". A light transmitter for a light wave having an allocated wavelength is provided in each station. A light signal going out of the light transmitter passes through a star coupler and reaches all the stations. Each station selects a light wave having a desired wavelength from all light waves received by the station. For instance, a specific wavelength .lambda.1 is allocated to a light transmitter provided in the station 1. On the other hand, in a case where a wavelength of signal for a light receiver in the station 1 to receive is .lambda.5 which is a wavelength specific to a signal transmitted by a light transmitter provided in a station 5, the light receiver selectively receives the signal having the wavelength. A function required to an optical filter is bidirectional wavelength multiplexing for light waves having wavelengths of .lambda.1 and .lambda.5. Conventionally a dielectric multilayered film filter has been used for this optical filter.
Configuration of an optical filter based on the conventional technology was as described above. Several problems in the conventional type of optical filter have degraded operations and characteristics of the system and also complicated the configuration.
One of the problems relating to the example of the conventional technology 1 is that a dielectric multilayered film filter has a large passage loss and many optical parts are used, which makes it difficult to assemble the optical filter. Furthermore an optical signal once goes out of an optical fiber into a space, passes through a lens or a dielectric multilayered film, and then goes into an optical fiber again, so that displacement of the light axis easily occurs, and if displacement of the light axis should occur, a severe accident such as breakage of an optical cable which is a trunk line may easily occur.
One of the problems relating to the example of the conventional technology 2 occurs in a ring type of network in a case where two or more light waves having different wavelengths are allocated to a station with increased line demands. However, two light waves having different wavelengths can not be dropped nor added by the optical filter shown in FIG. 30 simultaneously.
In the optical filter shown in FIG. 30, it is extremely difficult to achieve the refractive index of 100% for the fiber gratings 310a and 310b. When a coupling parameter .kappa.L is 2, R is 93%. In this step, of the light waves each sent from the light transmitter 312 and having a wavelength of .kappa.5 (called an adding light), those not reflected and passing therethrough, equivalent to 7% of all the light waves, may go into the light receiver 313 (This light is called crosstalk light). The light receiver 313 receives a light wave coming in from the terminal 315a and having a wavelength of .lambda.5 (this light is called dropping light). Namely an adding light from the transmitter 312 may cause crosstalk with a dropping light to be received by the receiver 313, which disadvantageously degrades the receiving characteristics.
In FIG. 30, if there are no fiber gratings 310a, 310b, of the power Pa of the adding light coming in from the terminal 316c, a ratio of a power added to the terminal 315b vs a power outputted to the terminal 315a is defined as isolation .eta..
Namely: EQU .eta.=(Power outputted to the terminal 315a)/(Power outputted to the terminal 315b) (1)
In a case where the refractive index adjusting sections 314a and 314b can be manufactured so that a length of a light path in the 3-dB coupler 311a is completely identical to that of the 3-dB coupler 311b, .eta. is zero (0), but in the manufacturing technology currently available, .eta. can be suppressed at most to a range from 0.1 to 0.01. Herein, in a case where an excessive loss in all light paths is ignored, power of the adding light coming in from the terminal 316c and going into the terminal 315b is expressed by the expression of Pa (1-R) / (1-.eta.). On the other hand, of power Pd of a light wave coming in from the terminal 315a, power of a dropping light outputted to the terminal 315b is expressed by the expression of Pd / (1-.eta.)Then, a ratio of crosstalk light vs. dropping light, namely the crosstalk X is given by the following expression: EQU X=Pa (1-R) / (Pd) (2)
When R is 93% and Pa is equal to Pd, X is 0.07 (=-11.6 dB).
The power penalty PP when crosstalk occurs in a state where a difference .DELTA. between an optical frequency of an adding light and that of a dropping light is zero (0) and polarization of the former is identical to that of the latter is expressed by the following expression: EQU PP=-10 log (1-4.multidot..sqroot.X) (3)
Namely, when X is 0.02, a power penalty of up to 3.6 dB is generated.
FIG. 31 shows a result of an experiment carried out using a 10 Gbit/s light transfer device to know a power penalty against crosstalk X. In this figure, a black circle indicates a value obtained by the experiment and a solid line indicates a value by computing according to the expression (1) . A result of the experiment well coincided with the computed value, and it was confirmed that a power penalty of 1 dB is generated against crosstalk of only -25 dB. To suppress a power penalty to, for instance, 0.2 dB or less, the crosstalk must be suppressed under -39 dB. The refractive index R to satisfy the requirement is computed as 99.99% from the expression (2). When viewed from a viewpoint of actual conditions in production of fiber gratings, it is extremely difficult to satisfy this requirement.
In a ring type of network, sometime it is required to switch a wavelength of dropped and adding light wave to a given wavelength in association with fluctuation in demands for each line. However, in the optical filter shown in FIG. 30, it is impossible to freely select a wavelength.
An optical filter required for a star-shaped network can be formed with the dielectric multilayered film as shown in FIG. 29, a section between an input fiber and an output fiber in the dielectric multilayered film optical filter is formed with a lens system, so that not only the insertion loss is large, but also the assembly is difficult, which is disadvantageous for mass production thereof.
A first object of the present invention is to provide an optical branch circuit in which a passage loss due to wavelength multiplexing is small and displacement of light axis never occurs.
A second object of the present invention is to insure a communication path for communication between terminal stations with each other by increasing terminal stations each accommodated in a wavelength multiplexed optical transfer system and separating a troubled portion therefrom even if any trouble occurs in the transfer path.
A third object of the present invention is to provide a construction in which a passage loss due to wavelength multiplexing is small and a number of wavelengths for a specified path can be obtained as many as possible in the optical branch circuit in which displacement of light axis never occurs.
A fourth object of the present invention is to provide an optical dropping/adding circuit which can communicate with any other station.
A fifth object of the present invention is to provide an optical filter which can multiplex a plurality of light waves by dropping and adding them.
A sixth object of the present invention is to provide an optical filter which can suppress a frequency of crosstalk and of which the transfer characteristics is not degraded even in a case where a wavelength of a dropping light wave is the same as that of an adding light wave.
A seventh object of the present invention is to provide an optical filter which can select a wavelength to be dropped and added for multiplexing.
An eighth object of the present invention is to provide an optical filter in which a loss is small when bidirectional WDM is executed, and also which can easily be assembled and is suited to mass production.
A wavelength multiplexed light transfer unit according to the present invention comprises first, second, and third optical filters each having a first terminal into which a light signal having a specified wavelength .lambda.1 and a light signal having a wavelength other than .lambda.1 are inputted; a second terminal which outputs the light signal having a wavelength .lambda.1 inputted into this first terminal; a third terminal into which the light signal having a wavelength other than .lambda.1 is inputted; and a fourth terminal which outputs the light signal having a wavelength other than .lambda.1 inputted to the first terminal, and also each outputting the light signal having a wavelength other than .lambda.1 inputted into the third terminal to the second terminal; in which the third terminal of the first optical filter and the fourth terminal of the second optical filter are connected to each other; the third terminal of the second optical filter and the fourth terminal of the third optical filter are connected to each other; and the third terminal of the third optical filter and the fourth terminal of the first optical filter are connected to each other.
In a wavelength multiplexed light transfer system according to the present invention, terminal station equipments each having a light transmitting/receiving device for transmitting or receiving a light signal having a specified wavelength .lambda.1 and that having a wavelength other than .lambda.1 through the wavelength multiplexed light transfer unit vertically connected to each other are communicated with each other.
A wavelength multiplexed light transfer unit according to the present invention comprises, a first filter having a first terminal into which a light signal having a specified wavelength .lambda.1 and a light signal having a wavelength other than .lambda.1 are inputted; a second terminal which outputs the light signal having a wavelength of .lambda.1 inputted into this first terminal; a third terminal into which the light signal having a wavelength other than .lambda.2 is inputted; and a fourth terminal which outputs the light signal having a wavelength other than .lambda.1 inputted to the first terminal; and second and third filters each having: a first terminal into which a light signal having a specified wavelength .lambda.2 and a light signal having a wavelength other than .lambda.2 are inputted; a second terminal which outputs the light signal having a wavelength of .lambda.2 inputted into this first terminal; a third terminal into which the light signal having a wavelength other than .lambda.2 is inputted; and a fourth terminal which outputs the light signal having a wavelength other than .lambda.2 inputted to the first terminal; in which the third terminal of the first optical filter and the fourth terminal of the second optical filter are connected to each other; the third terminal of the second optical filter and the fourth terminal of the third optical filter are connected to each other; and the third terminal of the third optical filter and the second terminal of the first optical filter are connected to each other.
A wavelength multiplexed light transfer unit according to the present invention comprises, an optical filter having a first terminal for receiving and inputting a light wavelength multiplexed signal having a wavelength within a specified wavelength band .lambda.B1 allocated to a station for receiving as well as a light wavelength multiplexed signal having a wavelength outside the specified wavelength band .lambda.B1, a second terminal for outputting the light wavelength multiplexed signal having a wavelength within the wavelength band .lambda.B1 inputted into the first terminal, and a third terminal the light wavelength multiplexed signal having a wavelength outside the wavelength band .lambda.B1 inputted into the first terminal; a light receiver into which the light wavelength multiplexed signal outputted to the second terminal of the optical filter is inputted; a light transmitter for outputting a light wavelength multiplexed signal having a wavelength for transmission within a wavelength band allocated from the station to a receiving station; and a directional coupler for synthesizing the light wavelength multiplexed signal having a wavelength outside the wavelength band .lambda.B1 outputted from the third terminal of the optical filter and the light wavelength multiplexed signal outputted from the light transmitter and outputting the synthesized signal for transmission.
A wavelength multiplexed light transfer unit according to the present invention comprises, an optical filter having a first terminal for receiving a light wavelength multiplexed signal having a wavelength within any of N pieces of wavelength band from .lambda.B1 to .lambda.BN as well as a light wavelength multiplexed signal having a wavelength outside the wavelength bands, a second terminal for outputting a light wavelength multiplexed signal having a wavelength within wavelength bands from .lambda.B1 to .lambda.BN inputted into this first terminal, a third terminal for inputting light wavelength multiplexed signal having a wavelength within the wavelength bands from .lambda.B1 to .lambda.BN, and a fourth terminal for outputting the light wavelength multiplexed signal having a wavelength outside the wavelength bands inputted into the first terminal as well as the light wavelength multiplexed signal having a wavelength within the wavelength bands from .lambda.B1 to .lambda.BN inputted into the third terminal; a light receiver for receiving the light wavelength multiplexed signal outputted to the second terminal of the optical filter; and a light transmitter for outputting the light wavelength multiplexed signal having a wavelength within the wavelength bands from .lambda.B1 to .lambda.BN inputted to the third terminal of the optical filter.
A wavelength multiplexed light transfer unit according to the present invention comprises a grating light guide path having a plurality of reflected wavelength formed in the identical grating light guide path as an optical filter.
A wavelength multiplexed light transfer unit according to the present invention comprises, an optical filter having a first terminal for receiving a light signal having a wavelength within a specified wavelength band .lambda.B1 as well as a light signal having a wavelength outside the wavelength band .lambda.B1, a second terminal for outputting the transmitted light signal having a wavelength within the wavelength band .lambda.B1 inputted into this first terminal, a third terminal for receiving a light signal having a wavelength within the wavelength band .lambda.B1, and a fourth terminal for outputting the light signal having a wavelength outside the wavelength band .lambda.B1 inputted into the first terminal as well as the light signal having a wavelength within the wavelength band .lambda.B1 inputted into the third terminal; a light receiver for receiving a light signal outputted to the second terminal of the optical filter; a light transmitter for outputting a light signal to the third terminal of the optical filter; and a light frequency control means for controlling the light transmitter so that the light transmitter will oscillate a light having a wavelength displaced by a specified value from a wavelength of a light signal received by the light receiver.
A wavelength multiplexed light transfer unit according to the present invention comprises, a first optical filter having a first terminal for receiving a light signal having a specified wavelength .lambda.1 as well as a light signal having a wavelength other than the wavelength .lambda.1, a second terminal for outputting the light signal having a wavelength .lambda.1 inputted into this first terminal, a third terminal for outputting a light signal having a wavelength other than the wavelength .lambda.1 inputted into the first terminal; a second optical filter having a fourth terminal for receiving the light signal having a wavelength other than the wavelength .lambda.1 outputted from the third terminal of this first optical filter, a fifth terminal for receiving the light signal having the specified wavelength .lambda.1 as well as that having a wavelength other than the wavelength .lambda.1, and a sixth terminal for outputting the light signal having a wavelength other than the wavelength .lambda.1 inputted into the fourth terminal as well as a transmitted light signal having a wavelength .lambda.1 inputted into the fifth terminal; a light receiver for receiving a light signal outputted to the second terminal of the first optical filter; and a light transmitter for outputting a light signal to the fifth terminal of the second optical filter.
A wavelength multiplexed light transfer unit according to the present invention comprises, a first optical filter having a first terminal for receiving a light signal having a specified wavelength .lambda.1 as well as a light signal having a wavelength other than the wavelength .lambda.1, a second terminal for outputting the light signal having a wavelength .lambda.1 inputted into this first terminal, a third terminal for outputting a light signal having a wavelength other than the wavelength .lambda.1 inputted into the first terminal; and a second optical filter having a fourth terminal for receiving the light signal having a wavelength other than the wavelength .lambda.1 outputted from the third terminal of this first optical filter, a fifth terminal for receiving the light signal having the specified wavelength .lambda.1 as well as that having a wavelength other than the wavelength .lambda.1, and a sixth terminal for outputting the light signal having a wavelength other than the wavelength .lambda.1 inputted into the fourth terminal as well as a transmitted light signal having a wavelength .lambda.1 inputted into the fifth terminal; in which the third terminal of the first optical filter and the fourth terminal of the second filter are connected to each other with a wavelength selective reflector in which a center wavelength of reflection is .lambda.I.
A wavelength multiplexed light transfer unit according to the present invention comprises, a first optical filter having a first terminal for receiving a light signal having a specified wavelength .lambda.2 as well as a light signal having a wavelength other than the wavelength .lambda.2, a second terminal for outputting the light signal having a wavelength .lambda.2 inputted into this first terminal, a third terminal for outputting a light signal having a wavelength other than the wavelength .lambda.2 inputted into the first terminal; a second optical filter having a fourth terminal for receiving the light signal having a wavelength other than the wavelength .lambda.2 outputted from the third terminal of this first optical filter, a fifth terminal for receiving the light signal having the specified wavelength .lambda.2, and a sixth terminal for outputting the light signal having a wavelength other than the wavelength .lambda.2 inputted into the fourth terminal as well as a transmitted light signal having a wavelength .lambda.2 inputted into the fifth terminal, a third optical filter having a seventh terminal for receiving a light signal having a specified wavelength .lambda.1 as well as a light signal having a wavelength other than the wavelength .lambda.1, an eighth terminal for outputting the light signal having a specified wavelength .lambda.2 as well as a light signal having a wavelength .lambda.1 inputted into the seventh terminal, a ninth terminal for receiving a light signal having a wavelength .lambda.2 outputted to the eighth terminal, and a tenth terminal for outputting a light signal having a wavelength other than the wavelength .lambda.1 received from the seventh terminal; and a fourth optical filter having a twelfth terminal for receiving the light signal having a wavelength other than the wavelength .lambda.1 outputted from the tenth terminal of the third optical filter, a thirteenth terminal for receiving the light signal having the specified wavelength .lambda.1 as well as the light signal having a specified wavelength .lambda.2, a fourteenth terminal for outputting the light signal having a wavelength .lambda.1 received from the thirteenth terminal as well as a light signal having a wavelength other than the wavelength .lambda.1 received from the twelfth terminal, and an eleventh terminal for outputting the light signal having a wavelength .lambda.2 received from the thirteenth terminal; in which the second terminal and the ninth terminal are connected to each other, and the fifth terminal and the eleventh terminal are connected to each other.
A wavelength multiplexed light transfer unit according to the present invention comprises, a first light circulator having a first port for receiving N waves of light wavelength multiplexed signal having specified wavelengths from .lambda.1 to .lambda.N, a second port for outputting the light wavelength multiplexed signal inputted into the first port, and a third port for outputting the light wavelength multiplexed signal inputted into the second port; a directional coupler having a first terminal for receiving a light wavelength multiplexed signal having a wavelength within any of wavelength bands from .lambda.1 to AN outputted from the second port of the first light circulator and also outputting a light wavelength multiplexed signal having a wavelength within any of wavelength bands from .lambda.1 to AN to the second port of the first light circulator, a second terminal for receiving a light wavelength multiplexed signal, a third terminal and a fourth terminal each for dividing a light signal having a wavelength within any of the wavelength bands .lambda.1 to .lambda.N inputted into the first and second terminals into two portions, outputting the divided light signal, and receiving light signals having wavelengths from .lambda.1 to .lambda.N, the directional coupler outputting a synthesized light signal to the second terminal if a phase of a light signal inputted into the third terminal and returning the first terminal is reversed to that of a light signal inputted into the fourth terminal and returning to the first terminal, and also outputting a synthesized light signal to the first terminal if the phases of the two signals are identical, outputting a synthesized light signal to the first terminal if a phase of a light signal inputted into the third terminal and returning to the second terminal is reversed to that of a light signal inputted into the fourth terminal and returning to the second terminal, and also outputting a synthesized light signal to the second terminal if the phases of the two signals are identical; first to N-th wavelength selective reflectors reflecting light signals having wavelengths from .lambda.1 to .lambda.N and respectively connected to the third terminal of the directional coupler; first to N-th light phase shifters each provided in correspondence to each of the first to N-th wavelength selective reflector and shifting a phase of a light signal passing therethrough; N+1-th to 2N-th wavelength selective reflectors reflecting light signals having wavelengths from .lambda.1 to .lambda.N and respectively connected to the fourth terminal of the directional coupler; a light phase shifter control circuit for controlling a shaft rate for each of the first to N-th light phase shifters so that a phase of a light signal outputted from the first or second terminal of the directional coupler to the third and fourth terminals, reflected by any of the first to Nth wavelength selective reflectors, inputted into the third terminal and returning to the first or second terminal will be reverse to that of a light signal reflected by any of the N+1-th to 2N-th wavelength selective reflectors, inputted into the fourth terminal and returning to the first or second terminal in a case of a light signal to be branched, and also so that the former will be the same as the latter in a case of a light signal to be passed therethrough; a second light circulator having a first port for receiving a light wavelength multiplexed signal outputted from the second terminal of the directional coupler and also outputting a light wavelength multiplexed signal to the second terminal of the directional coupler, a second port for outputting a light wavelength multiplexed signal inputted into this first port, and a third port for receiving a light wavelength multiplexed signal and outputting the signal to the first port; a light receiver for receiving the light wavelength multiplexed signal outputted to the second port of the second light circulator; and a light transmitter for outputting a light wavelength multiplexed signal to the third port of the second light circulator.
A wavelength multiplexed light transfer unit according to the present invention comprises, a first optical filter having a first terminal for receiving and outputting a light signal having a specified wavelength .lambda.i, a light signal having a wavelength .lambda.J, and a light signal having a wavelength other than the wavelengths .lambda.i and .lambda.j, a second terminal for outputting the light signal having a wavelength .lambda.i inputted into this first terminal and receiving a light signal having a wavelength .lambda.i, and a third terminal for outputting a light signal having a wavelength other than the wavelength .lambda.i inputted into the first terminal, the first optical filter outputting the light signal having a wavelength .lambda.i inputted into the second terminal to the first terminal; a second optical filter having a fourth terminal for receiving the light signal having a wavelength other than wavelength .lambda.i outputted from the third terminal of the first optical filter and a fifth terminal for outputting the light signal having a wavelength .lambda.j inputted into this fourth terminal; a light transmitter for outputting a light wavelength multiplexed signal for the second terminal of the first optical filter; and a light receiver for receiving the light wavelength multiplexed signal outputted to a second terminal of the second optical filter.
A wavelength multiplexed light transfer unit according to the present invention forms an optical filter with a grating light guide path in which a wavelength of a first reflected light is shorter than that of a second reflected light as the first optical filter.
A wavelength multiplexed light transfer unit according to the present invention comprises, a first optical filter having a first terminal for receiving and outputting a light signal having a specified wavelength .lambda.i, a light signal having a wavelength .lambda.j and a light signal having a wavelength other than the wavelengths .lambda.i, .lambda.j, a second terminal for outputting the light signal having the wavelength .lambda.i inputted into this first terminal, and a third terminal for outputting a light signal having a wavelength .lambda.i inputted into the thirst terminal, the first optical filter outputting the light signal having the wavelength .lambda.j inputted into the third terminal to the first terminal; a second optical filter having a fourth terminal for receiving a light signal having a wavelength .lambda.i outputted from the second terminal of the first optical filter and a fifth terminal for outputting the light signal having the wavelength .lambda.i inputted into this fourth terminal; a light transmitter for outputting a light wavelength multiplexed signal to the third terminal of the first optical filter; and a light receiver for receiving the light wavelength multiplexed signal outputted to the fifth terminal of the second optical filter.
A wavelength multiplexed light transfer unit according to the present invention formes an optical filter with a grating light guide path in which a wavelength of a first reflected light is shorter than that of a light signal transmitted from the light transmitter as the first optical filter.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.